This invention refers to a suction system for reciprocating type hermetic compressor used in refrigeration appliances. The suction systems used in reciprocating type hermetic compressors normally consist of a set which includes chambers, ducts, plates and deflectors, the function of which is to damp the pulsations of the refrigerating gas, making the gas flow as uniform as possible.
These units are normally manufactured of insulating plastic material, in order to avoid that the refrigeration gas becomes overheated when coming into contact with hot metallic components of the compressor, mainly the head and the cylinder. This overheating results in a reduction of the refrigeration gas density which, in turn, brings about a reduction of the flow of mass admitted and compressed by the compressor and its consequent efficiency drop.
Although the known suction systems reduce up to a certain degree the refrigeration gas overheating in suction, they are still deficient and, above all, problematic with regard to its manufacture.
A known system is presented by the U.S. Pat. No. 4,370,104, which describes a suction muffler unit consisting of two parts of plastic material assembled in the block. One of the parts has a cylindrical form with a cup-shaped end and this end has an opening for the introduction of a metallic tube for suction connected to the cylinder head. The other part, also cup-shaped, is assembled on the open end of the first part and presents a nozzle projected towards the compressor housing suction tube.
One deficiency of this muffler is that it does not prevent the refrigeration gas from being heated along the suction metallic tube and in the suction chamber inside the head.
As to the filtering, this muffler of the prior art presents great problems due to the fact that it is formed in one single volume (chamber). And due to this fact, the loss of filtering in the muffler is approximately 40dB/decade, which corresponds to the filtering effect of a volume and a tube.
Another known system is the one of U.S. Pat. No. 4,449,610. This one presents a suction muffler consisting of a plastic material body with two chambers interconnected by a slot and directly assembled on the compressor head by means of two small tubes provided with adequate sealing means.
Similarly to the above described system, this other muffler also shows deficiencies regarding the insulation of gas in suction, since it does not avoid that the refrigerating gas is heated in the suction chamber.
Another deficiency of this second system is that in order to obtain a satisfactory acoustic effect, it tubes have a very reduced diameter, which results in a considerable restriction of refrigerating gas flow, increasing the energy losses in the suction.
Another suction system is, further, described in the patent document EPO 195 486 A2. This system consists of one suction chamber made of synthetic material as a separate part of the head so as to reduce the heat transfer from the head to the suction chamber. This chamber is formed integrally with the suction muffler and takes the shape of an appendage. An additional heat transfer reduction for the refrigerating gas is obtained by means of an elastic connection between the suction-tube and the suction muffler. Although this suction system reduces considerably the heat transfer from the head to the refrigerating gas, it presents serious problems regarding the oil circulation, since it does not provide an oil separator, a necessary element in direct suction systems. The accumulation of oil in the suction chamber may cause oil suction to the cylinder, resulting in damage of the valves and breakage of the crankshaft.
Another deficiency of this system refers to its low efficiency as an acoustic filter when restrictions are imposed on the gas flow by the interconnection holes of the two suction muffler volumes, since these restrictions produce a low acoustic impedance in relation to the pressure loss, imposed on the suction gas. This low acoustic impedance results in a weak attenuation of suction noise.